1. Field of the Invention
The subject invention is an Aided Inertial Navigation System (AINS) configured for land survey applications and having the form and function of a standard GPS survey instrument. The invention uses an AINS as a navigational reference, which makes it possible to survey areas where GPS signals may be missing for time intervals of varying duration, or indefinitely, due to building obstruction, operation inside a building, tree foliage and or a dense tree canopy. An AINS that is normally aided with a radio positioning system such as GPS but loses position aiding as a result of signal blockage enters into a dead reckoning navigation mode, and requires some alternative form of aiding to control the position error drift. A typical source of velocity aiding is a zero velocity update in which the AINS is held stationary periodically to reset the accumulated velocity error to zero. The subject invention implements an AINS in a format that is similar to a standard GPS survey instrument, and uses a novel method of zero velocity aiding to navigate through GPS outages caused by signal blockage.
2. Background of the Invention
The Trimble 4700 Site Surveyor is an example of a GPS land survey instrument that is similar to the present invention. Similar products are available from other GPS manufacturers. The 4700 Site Surveyor has a staff with a GPS antenna at the top end and a simple spike at the bottom end. A hand-held control and display unit (CDU) can be alternatively held by the surveyor or mounted to the staff at the approximate midpoint. Modern GPS receivers for surveying are small enough to be mounted to the staff as well. Alternatively the receiver can be carried with the batteries that power the unit in a backpack carried by the surveyor. The surveyor walks to each point to be surveyed, places the spike at the bottom end on the point, and either records a position computed by the receiver or “occupies” the point for a period of time during which the receiver records data for post-survey processing.
The disclosed WSN is designed to have a “look and feel” similar to a typical GPS survey instrument. It is believed that the WSN will gain acceptance among surveyors fairly quickly because of its similarity to industry accepted GPS survey instruments. The only additional field procedure that a surveyor must conduct is to manipulate the WSN like a walking stick when GPS drops out.
In operation, the surveyor uses the WSN for dead reckoning navigation when GPS signals become obstructed, as might occur inside or between buildings or in a forested area. The surveyor walks a survey trajectory and uses the WSN as a positioning system to survey positions along the trajectory. Such survey trajectories sometimes pass through areas where no GPS signals are available. The WSN must therefore navigate in a dead-reckoning mode with as little position drift as possible.